The Evaluation of Planting Direction on the Consumption of Resources and Soil Nutrients in Sunflower (Helianthus annus L.) and Cow Pea (Phaseolus vulgaris L.) Intercropping

Introduction Agriculture plays an essential role in providing food, and in order to achieve sustainability in the agricultural sector, resources must be used in the best possible way. In order to achieve the maximum possible yield, it is necessary for the crop plant to use the environmental factors, water, nutrients, light, and carbon dioxide, with the maximum possible efficiency. The maximum use of the required factors for growth is achieved only when the plant community exerts maximum pressure on these factors. In general, intercropping is one of the ways to achieve sustainable agriculture, with higher yields without increasing agricultural inputs, absorption, and environmental factors productivity. Researchers for the intercropping of corn and mung bean have reported that the mixed cultivation systems used environmental resources more effectively compared to the sole cropping of corn and mung bean. For this reason, nowadays, many plants, especially legumes, are cultivated in an intercropping form due to their ability to fix nitrogen. Due to the lack of resources regarding the effect of planting direction on plant yield, this study was conducted in order to evaluate resources and soil nutrients by changing the planting direction and replacing the intercropping system of the sunflower with cowpea. Materials and Methods This research was conducted in the field of the Agricultural Research Station of Zabol University during 2015-2016. The experiment was performed as a split-plot based on a randomized complete block design with three replications at the Research Farm of the Agricultural Research Institute of Zabol University.  The main factor was two levels of planting direction (North-South and East-West), and the secondary factor was intercropping system in five levels, including (100% pure sunflower), (100% pure cowpea ), (50% sunflower + 50% cowpea ) (25% cowpea  + 75% sunflower) and (75 % cowpea  + 25%sunflower) were considered. Data for studied traits were measured as follows: radiation, temperature, volumetric humidity, calcium, phosphorus, magnesium, potassium, and the land equality ratio.  Statistical analysis including, analysis of variance and mean comparisons (least significant difference (LSD) test at the 5% level), were applied to evaluated traits. Results and Discussion The maximum absorption of photosynthetically active radiation (PAR) was in the east-west cultivation direction (77.90%) compared to the north-south treatment, which was 24.6% more than the north-south direction. The analysis of variance indicated that the cultivation direction and intercropping systems on the amount of phosphorus in the soil after harvest were significant at 1% probability level. The comparison of means treatments showed that the amount of phosphorus in the soil in the direction of east-west cultivation was 15% higher compared to the direction of north-south cultivation. The highest amount of soil potassium was obtained in the east-west treatment and the intercropping system of 50% sunflower plus 50% cowpea (24.7 ppm). The lowest amount of soil potassium (16.15 ppm) was obtained in the treatment of east-west cultivation and the intercropping system of 75% sunflower plus 25% cowpea. The relative advantage of intercropping is expressed by the land equivalent ratio. The increase in the ratio of equal land per unit shows the relative usefulness of intercropping compared to sole cropping of each of the mixed components. The comparison of means of the intercropping system showed that among the treatments, the mixture of 75% sunflower plus 25% cowpea had the highest land equivalent ratio (2.54). Conclusion It seems that in order to maintain humidity make maximum use of limited water resources, and obtain high yield, the intercropping system of 75% sunflower plus 25% cowpea and planting direction the prevailing wind of the region (east-west) should be suitable for this region and regions with similar climate and windy conditions. Acknowledgments We would like to thank the chairman and the respected staff of the Agricultural Research Institute of Zabul University, who sincerely accompanied us in the implementation of this thesis.